3 ms·

[EDIT: Below I have demonstrated a slow brain rot that has robbed me of my ability to do basic dimensional analysis. My lecturers are spinning in their graves,

[EDIT: Below I have demonstrated a slow brain rot that has robbed me of my ability to do basic dimensional analysis. My lecturers are spinning in their graves, least of all because I forgot that the kilogram is between the gram and the tonne. Luckily I was off by 3 orders of magnitude in both directions so I guess it sort of balances out?] The heat absorption is a good point, I don't know what native foliage is like to live in compared to the concrete hell you'd be left with without lawns. But, I find it hard to imagine that turf grass in climates where it can't survive without massive irrigation and ceaseless human intervention sequesters more carbon than it costs to maintain. The numbers I've quickly gathered are all over the place, but given that: - The average Californian lawn is ~500 sqm [0] - Grass sequesters ~ 85g of carbon per sqm per year, or 42 tonnes per year [1] - As of 2011 the average Californian household uses 190 gallons of potable water a day on landscaping [2] - About 0.004 metric tonnes of carbon is generated processing 1000 gallons of potable water or 0.76 tonnes per day of watering [3] So, the average Californian lawn sequesters 42 tonnes of carbon a year, while the energy cost of irrigating it emits about 277 tonnes. This is all quick back of an envelope math, but the carbon cost of irrigating a lawn where it wasn't meant to grow is massively larger than the amount that the grass sequesters. It's honestly bad enough that you could tear up every lawn in California and not even bother replacing them with native foliage, and it would still result in a net decrease in carbon emissions. [0]: https://www.homeadvisor.com/r/average-yard-size-by-state/ https://www.homeadvisor.com/r/average-yard-size-by-state/ [1]: https://www.researchgate.net/publication/282543110_Modeling_Carbon_Sequestration_in_Home_Lawns https://www.researchgate.net/publication/282543110_Modeling_... [2]: https://www.kqed.org/lowdown/11525/how-much-water-do-californians-use-and-what-would-20-percent-less-look-like https://www.kqed.org/lowdown/11525/how-much-water-do-califor... [3]: http://leansixsigmaenvironment.org/index.php/how-much-impact-does-one-gallon-of-water-in-your-home-or-business-have-on-the-environment/ http://leansixsigmaenvironment.org/index.php/how-much-impact...

leto_ii 4y ago
> - The average Californian lawn is ~500 sqm [0] > - Grass sequesters ~ 85g of carbon per sqm per year, or 42 tonnes per year [1] 500 * 85g/m2 = 42500 g/m2 - that's 42.5 kg, not 42.5 tonnes. I haven't checked your original sources, but based on the numbers you provided you're off by 3 orders of magnitude. Intuitively this makes sense, I mean 42 tonnes is a huge amount of carbon to sequester in a lawn. Where would all that mass go? It would mean that the average lawn produces >> 42 tonnes of grass per year.
- DoughnutHole 4y ago
  You're completely right that was a misstep, I was thinking that seemed high but didn't really think it through - that would be a ludicrous mass of trimmings... So the sequestration is even lower.
engineer_22 4y ago
Imagining 42 tons of yard waste piling up outside every year, seems a little off the mark. 500 sqm X 85 g/yr is 42.5 kg/yr Also, 190 gpd / 1000 gal = 0.19 kgal per day 0.004 tons per kgal per day x 0.19 x 365 days = .277 tons per year Therefore 0.0425 tons sequestered, 0.277 tons produced by irrigation. The ratio of carbon sequestered to carbon produced on irrigation is the same as your original calculations. But I think the major source of carbon won't be in irrigation, but in the maintenance, mowing the lawn, transportation for the landscaper, transporting pesticides and fertilizers, etc.
a-dub 4y ago
[3] seems like a bit of a stretch to me. we know for a fact that different communities have different energy needs for moving water around based on simple geography. we also know that different communities have different electricity sources providing municipal power. (the bay area's primary water system makes use of hydroelectric power, for example). finally, i'm not convinced that the marginal cost per gallon makes up the total cost of moving water around. much of the costs are fixed infrastructure costs that don't necessarily move with utilization. here's a thought experiment: assume infinite clean electricity and desalination capacity in the face of an overcarbonated atmosphere and climate change. do you install and irrigate as much vegetation as you can or do you rip it all out and put in rocks?

leto_ii 4y ago

> - The average Californian lawn is ~500 sqm [0] > - Grass sequesters ~ 85g of carbon per sqm per year, or 42 tonnes per year [1] 500 * 85g/m2 = 42500 g/m2 - that's 42.5 kg, not 42.5 tonnes. I haven't checked your original sources, but based on the numbers you provided you're off by 3 orders of magnitude. Intuitively this makes sense, I mean 42 tonnes is a huge amount of carbon to sequester in a lawn. Where would all that mass go? It would mean that the average lawn produces >> 42 tonnes of grass per year.

DoughnutHole 4y ago
You're completely right that was a misstep, I was thinking that seemed high but didn't really think it through - that would be a ludicrous mass of trimmings... So the sequestration is even lower.

engineer_22 4y ago

Imagining 42 tons of yard waste piling up outside every year, seems a little off the mark. 500 sqm X 85 g/yr is 42.5 kg/yr Also, 190 gpd / 1000 gal = 0.19 kgal per day 0.004 tons per kgal per day x 0.19 x 365 days = .277 tons per year Therefore 0.0425 tons sequestered, 0.277 tons produced by irrigation. The ratio of carbon sequestered to carbon produced on irrigation is the same as your original calculations. But I think the major source of carbon won't be in irrigation, but in the maintenance, mowing the lawn, transportation for the landscaper, transporting pesticides and fertilizers, etc.

a-dub 4y ago

[3] seems like a bit of a stretch to me. we know for a fact that different communities have different energy needs for moving water around based on simple geography. we also know that different communities have different electricity sources providing municipal power. (the bay area's primary water system makes use of hydroelectric power, for example). finally, i'm not convinced that the marginal cost per gallon makes up the total cost of moving water around. much of the costs are fixed infrastructure costs that don't necessarily move with utilization. here's a thought experiment: assume infinite clean electricity and desalination capacity in the face of an overcarbonated atmosphere and climate change. do you install and irrigate as much vegetation as you can or do you rip it all out and put in rocks?